1. Field of the Invention
This invention relates to the field of particle concentrators, and more particularly to an apparatus and system for preconcentrating airborne particles to promote their detection. Specifically, the invention relates to a human portable particle preconcentrator system and apparatus that exhibits simple and reliable operation and is especially useful in conjunction with detecting compounds such as explosives, illegal drugs, other controlled substances and chemical agents. For purposes of this application, in the context of describing the claimed invention, the term particle is intended not to exclude vapor.
2. Description of the Related Art
Additional background information, supplemental to the information provided here, is found in U.S. Pat. No. 5,854,431 xe2x80x9cParticle Preconcentratorxe2x80x9d which is incorporated by reference herein in its entirety.
The detection of explosives, narcotics or other chemicals is a growing part of contraband detection. Recent years have seen rapid development of detectors capable of identifying the presence of explosives by capturing and identifying either vapors emanating from explosive materials or particles of explosive material, or both. Similarly, such detectors can also identify vapors and particles associated with other forms of contraband such as illegal drugs and other controlled substances. Such vapors and particles associated with contraband may be present and detectable on or near persons or objects that have been exposed to contraband materials and substances. Suitable detectors for this purpose include, but are not limited to, ion mobility spectrometers (IMS), electron capture detectors, and chemi-luminescence-based systems.
Detection of explosives, narcotics or other contraband substances demands reliable and convenient means for collecting and analyzing sample. For detection modalities such as those mentioned above, however, a challenge exists relating to accurately detecting and identifying target substances when only a small amount or small concentration of target chemical is present on or in proximity to a test subject. Often, collecting sample involves processing large volumes of diluent (for example, air) in order to obtain sufficient target chemicals for detection. The preconcentrator disclosed in the ""431 patent offers one means for collecting trace amounts of target chemical in dilute concentration. There, target chemical is adsorbed onto at least one screen adapted to capture and concentrate particulate material and/or vapors entrained in a main gas flow. Then, using a secondary carrier gas flow, the concentrated target chemical is moved to a detector. The ""431 device was designed to achieve the desired preconcentration of target chemicals while managing large amounts of air flow, in part, by using a system of chambers and valves. The present invention is simplified over the earlier technology and includes a number of features that are suited to convenient portability. For certain applications, the present invention offers a viable alternative to the preconcentrator described in the ""431 patent.
A logical advance in the field of contraband detection has been the development of commercial portable detection instruments having hand-held (or otherwise human-portable) operating capabilities. Commercial manufacturers of portable detectors (such as IMS) have begun tuning their instruments to identify contraband substances. As noted, though, in many situations, the amount of chemical(s) available for sampling is small or in low concentration. Current methods for increasing sample concentration include wiping a surface to collect particulate residue or vacuuming a surface to collect particles and/or vapor. In both sampling methods, the collected sample is usually deposited on a paper or other substrate, perhaps treated with Teflon(trademark) or another similar non-stick coating. According to one such method, sample collection involves physically rubbing (swiping) a substrate such as a felt on a surface of an object (herein referred to as a test subject) and then placing the substrate into the detector for analysis. An alternate sampling method is to vacuum the surface of a test subject (or the air around a test subject), pass the vacuumed air, containing sample, through a collector substrate, and again, place the collector substrate into the detector for analysis. In either case, these methods of sampling are time consuming and tedious, and they incur a cost for replacing the substrate. Additionally, especially where the swiping technique is used, there is a significant risk of sampling error if the amount of target chemicals present on a test subject is low, and the target chemicals are simply missed by the swipe. This is because it is generally impractical to swipe the entire surface of a test subject with a substrate.
Accordingly, a need remains for preconcentrator devices that are suitable to portable applications, that offer simplified operation as compared with existing technologies, and that effectively overcome challenges associated with obtaining and concentrating sample.
The human-portable preconcentrator system of the present invention provides a solution to the problems of collecting particulate and/or vapor sample and delivering it to the detector quickly. The system and apparatus disclosed here significantly reduce the overall collection and detection time by reducing, as compared with other technologies, the number of necessary manipulations and separate steps required in obtaining and testing sample. Additionally, the collection substrate within the human portable preconcentrator system need not be discarded or cleaned using labor-intensive techniques, prior to next use. Thus, the cost to obtain sample is reduced.
An advantage of the present invention is that it provides an apparatus for collecting particles entrained in a gas stream, the apparatus including: a body comprising a plenum, a first port through which gas with entrained particles can pass from a region outside of the body into the plenum, a second port and a third port; a fan adapted to draw gases through the plenum and second port; at least one pervious screen in a first position disposed across the second port; means for repositioning the at least one pervious screen to a second position disposed across the third port; and a connector adapted to permit joining the third port to a separate chemical detector.
Another advantage of the present invention is that it provides, a system for collecting and analyzing particles entrained in a gas stream, the system including elements similar to the apparatus just described, and also a detector adapted to draw gases from the plenum through the third port and perform chemical analysis of those gases.
Another advantage of the invention is that it provides a method of collecting and releasing target chemicals entrained in a gas, the method comprising the steps of: creating a first gas flow, having a first direction, to draw the gas with entrained target chemicals into a chamber and through at least one pervious screen whereby at least a portion of the target chemicals adhere to the at least one pervious screen, ceasing the first gas flow, and heating the at least one pervious screen thereby causing at least some of the chemicals that adhere to the at least one pervious screen to vaporize and evolve into the chamber.
Other objects, advantages and novel features will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.